$0.04 \times 0.0162 = ?$

When simplified,the value of the product $\left(1-\frac{1}{2}\right)\left(1-\frac{1}{3}\right)\left(1-\frac{1}{4}\right) \ldots\left(1-\frac{1}{n}\right)$ equals

If $x = \frac{4 \sqrt{ab}}{\sqrt{a} + \sqrt{b}}$,then what is the value of $\frac{x + 2 \sqrt{a}}{x - 2 \sqrt{a}} + \frac{x + 2 \sqrt{b}}{x - 2 \sqrt{b}}$ (when $a \neq b$)?

$\frac{3}{8}$ of $168 \times 15 \div 5 + ? = 549 \div 9 + 235$

What approximate value will come in the place of the question mark $(?)$ in the following expression? (You are not expected to calculate the exact value.)
$\frac{989}{34} \div \frac{65}{869} \times \frac{515}{207} = ?$

The value of $\left(\frac{0.051 \times 0.051 \times 0.051 + 0.041 \times 0.041 \times 0.041}{0.051 \times 0.051 - 0.051 \times 0.041 + 0.041 \times 0.041}\right)$ is